The present invention relates to seals for hydrogen cooled generators and particularly relates to a low flow fluid film seal including a brush seal for sealing between a hydrogen atmosphere on one side of a generator housing wall and generator bearing oil on the opposite side of the wall.
In hydrogen cooled generators, an end wall or casing surrounds a rotor and a seal is interposed between the housing wall and the rotor to seal between a hydrogen atmosphere on one side of the wall and oil on the opposite side of the housing wall, typically in the bearing cavity. Fluid film seals are conventionally used on hydrogen cooled generators as dynamic rotor seals with near-zero leakage. Turbine oil is the traditional working fluid of these seals because the turbine/generator unit must be supplied with turbine oil for its bearings. Fluid film seals are generally directed along the rotor by a pair of low clearance rings about the rotor shaft. In a typical system, this oil flow is allowed to fully enter the hydrogen environment within the housing wall or the bearing cavity on the opposite side of the wall. The oil that enters the hydrogen atmosphere entrains hydrogen gas, which is then removed from the generator and is vented from the system. Particularly, when oil enters the hydrogen side of the housing wall, it releases air dissolved in the oil into that environment and absorbs hydrogen, taking the hydrogen out of the system. The hydrogen consumption represents a constant and substantial expense to the user of the generator.
In other systems, which are completely separate from the bearing oil system, the system is saturated with hydrogen gas at the start of operation and thus absorbs less hydrogen during operation. However, these systems require substantial auxiliary equipment and longer rotors. Consequently, it is desirable to reduce the hydrogen consumption in the hydrogen cooling system.
In accordance with a preferred embodiment of the present invention, a low flow fluid film seal is provided which reduces the film flow of oil into the hydrogen atmosphere, hence reducing hydrogen consumption, with added benefits of facilitating manufacture and assembly and affording resistance to escape of hydrogen should sealing fluid pressure be lost, for example, during a fault event. To accomplish the foregoing, a low flow fluid film seal is provided between the rotor and the housing wall, segregating the hydrogen atmosphere on one side of the wall and the oil and air mix of the bearing cavity on the opposite side of the wall. In one preferred embodiment hereof, the low flow fluid film seal includes a combination of at least one seal ring and a brush seal. The brush seal comprises an annular array of bristles projecting inwardly from a seal casing for engagement at their tips with the rotor. The bristles are preferably formed of a Kevlar or polyester material. Preferably, the brush seal is carried by the seal casing and oil or another fluid for forming the fluid film is pumped into the sealing space at a higher pressure than the seal casing. The oil or fluid is constricted by the brush seal to create a low flow film seal. By reducing the flow of the fluid to a minimum required to maintain a complete circumferential film, hydrogen consumption is reduced. It will be appreciated that the film must be maintained at all operating conditions, including low speed, transients, during start-up and full speed operation.
Other advantages accrue to the use of brush seals in combination with a seal ring in sealing between a hydrogen atmosphere and a fluid cavity. For example, typically tight clearance seals are used. When such seals are used in conjunction with a brush seal, the tolerances can be loosened, rendering the manufacture of the seals much easier. Further, the seals are easier to assemble because the brushes are less sensitive than sealing rings to damage. They are also more tolerant of assembly misalignment because of their flexible nature. Still further, the brush seals afford substantial resistance to escape of the hydrogen gas through the seal should the sealing fluid pressure be lost as in a fault event, thereby minimizing the release of the explosive hydrogen gas.
In another preferred embodiment of the present invention, the low flow fluid film seal includes a pair of brush seals defining a cavity therebetween and in lieu of any other type of seal at that seal location. The cavity contains turbine oil supplied under pressure. With the tips of the brush bristles engaging the rotor and the turbine oil under pressure, a low flow film seal is provided between the rotor and the housing wall, eliminating the need for tight clearance seals. Thus, the low flow film seal comprised solely of brush seals lies between the seal cavity and the bearing cavity and outboard of an oil deflector seal.
In a preferred embodiment according to the present invention, there is provided in a hydrogen cooled generator having a rotor, a housing wall having a hydrogen atmosphere on one side, and a bearing in a bearing cavity containing a fluid, e.g., a liquid gas or a liquid/gas, on an opposite side of the housing wall, a low flow film seal between the rotor and the housing wall for substantially segregating the hydrogen atmosphere and fluid in the bearing cavity from one another, comprising a seal casing between the wall and the rotor, a seal ring carried by the casing about the rotor, a brush seal carried by the casing and having bristles engaging the rotor, the seal ring and the brush seal configured to provide a low flow film seal along the rotor substantially maintaining the hydrogen atmosphere and fluid on opposite sides of the casing segregated from one another.
In a further preferred embodiment according to the present invention, there is provided in a hydrogen cooled generator having a rotor, a housing wall having a hydrogen atmosphere on one side, and a bearing in a bearing cavity containing bearing oil, a low flow film seal between the rotor and the housing wall for segregating the hydrogen atmosphere and the oil and air mix in the bearing cavity from one another, comprising a seal casing between the wall and the rotor having an annular chamber opening inwardly toward the rotor and defined between a pair of axially spaced flanges, a pair of seal rings within the annular chamber, a spring maintaining the seal rings in engagement with the flanges and an annular brush seal carried by the seal casing having bristles engageable with the rotor for maintaining the seal between the rotor and the housing wall.
In a still further preferred embodiment according to the present invention, there is provided in a hydrogen cooled generator having a rotor, a housing wall having a hydrogen atmosphere on one side, and a bearing in a bearing cavity containing a fluid on an opposite side of the housing wall, a low flow film seal between the rotor and the housing wall for substantially segregating the hydrogen atmosphere and fluid in the bearing cavity from one another, comprising a seal casing between the wall and the rotor, a pair of axially spaced brush seals carried by the seal casing defining a chamber therebetween for receiving turbine oil under pressure, the bristles of each brush seal engaging the rotor, at least the brush seal on an inboard side of the seal casing forming a low flow film seal along the rotor substantially maintaining the hydrogen atmosphere and fluid on opposite sides of the seal casing segregated from one another.